6.20.4 Callback Options
If optparse's built-in actions and types just don't fit the
bill for you, but it's not worth extending optparse to define
your own actions or types, you'll probably need to define a callback
option. Defining callback options is quite easy; the tricky part is
writing a good callback (the function that is called when
optparse encounters the option on the command line).
Release 2.3.3, documentation updated on December 19, 2003.
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